Hepatitis E is an acute, self-limited hepatitis caused by hepatitis E virus (HEV). Although the disease is rarely diagnosed in industrialized countries, including the United States, hepatitis E is the most likely cause of acute hepatitis in adults worldwide and is highly endemic in Southeast Asia. On the basis of viral genetic and epidemiological features, the disease is divided into two forms, epidemic and autochthonous:

1. Outbreaks and sporadic cases of epidemic hepatitis E are common in developing countries and are caused by HEV genotypes 1 and 2. The epidemic form is associated with waterborne and fecal-oral transmission, with humans as the exclusive hosts. The epidemic form is rarely imported to the United States via travel.
2. In contrast, autochthonous hepatitis E is caused by genotypes 3 and 4, and pigs are the natural reservoir. Sporadic cases occur in developed countries when humans become accidental hosts. Rarely, transfusion-related HEV infection has occurred.

Acute hepatitis E may be asymptomatic, marked only by a rise in AST or ALT levels, or symptomatic (with or without jaundice). Asymptomatic infections are likely 10-30 times more common than symptomatic infections. Rare cases may have a subfulminant or fulminant course. Acute infection can be protracted and cholestatic, lasting for several weeks. Fulminant hepatic failure, defined as severe liver failure in the presence of encephalopathy that develops within 8 weeks of the onset of symptoms, is characterized by severe sudden liver cell dysfunction leading to encephalopathy, ascites, and coagulopathy in people with no underlying liver disease. Pregnant individuals are at increased risk for severe illness from HEV infection.